The invention arises as a result of a need in the art for a less complex and more wear-resistant solids reducing apparatus or mill which will operate with reduced consumption of energy compared to traditional mills including ball mills, hammer mills and the like. In the prior art, solids reducing devices, rapid wear of metal parts frequently occurs due to the fact that sliding contact of the parts with solids produces rapid abrasion of metal surfaces. The parts subjected to this wear must be frequently replaced or, to avoid this, high carbon steel or other comparably expensive materials must be used in the mills. Either way, the economics of the situation is unsatisfactory. Some examples of the known patented prior art are U.S. Pat. Nos. 3,455,517; 3,612,415 and 3,782,643.
The general objective of the present invention is to satisfy the above-stated need of the art by providing a simplified and comparatively inexpensive solids reducing apparatus which is constructed and operated in such a manner that all sliding contact between the solids and the metal elements which reduce the solids is virtually eliminated. Instead, the solids are fractured and reduced entirely by impact against coacting stationary and rotating reducing components and also by impact with other solids in the impact chamber of the apparatus. In effect, solids being reduced while gravitating into and through the impact chamber in a controlled manner are struck by a rotating hammer means and rebounded back and forth in a more-or-less zigzag path between moving hammer bars and stationary impact plates in an array surrounding the rotating hammer means. Abrading of the solids reducing elements is almost eliminated and low carbon steel may be employed for the impact elements. The wear ratio compared to conventional ball mills and hammer mills is about 1 to 10.
Almost the total energy consumed by the apparatus or mill is utilized in reducing the ore or other solids instead of being consumed as in the prior art in overcoming inertia of swinging impact members and in creating friction due to sliding contact of solids with crushing or other forms of disintegrating members.
In the invention, the stationary impact plates which surround the impact rotor are positioned relative to each other so that aggregates of the required size will gravitate from the impact chamber only after sufficient reduction of solids has occurred. The necessity for more complex adjustable discharge means is eliminated.
The apparatus is constructed so that impact elements on the rotor and in the stationary surrounding array are individually removable and replaceable at the exterior of the apparatus.
Another important feature of the invention is that the pure impact reduction system allows a comparatively slow rotor speed, such as 750 rpm in a large machine. This rotational speed will provide about 90 mph velocity for the tip of the rotor and propelled solids particles will attain speeds of 200-400 mph at times in the reduction or impact chamber. In effect, a fluidized bed of solids is created in the apparatus in which the particles impinge on themselves while rebounding back and forth between the rotor hammer bars and stationary surrounding impact plates. This operation is extremely efficient in reducing the solids to proper aggregate size in the minimum time with minimum energy consumed and minimum wear on the apparatus.
An optional forced air system constitutes a further feature of the invention by means of which a draft is induced through a collection chamber for fines and dust. With or without this feature, the larger aggregates gravitate through a funnel-like discharge means at the bottom of the main reducing chamber.
Other features and advantages of the invention will become apparent during the course of the following description.